29 research outputs found
Switching Plasmons: Gold NanorodāCopper Chalcogenide CoreāShell Nanoparticle Clusters with Selectable Metal/Semiconductor NIR Plasmon Resonances
Exerting control over the near-infrared
(NIR) plasmonic response
of nanosized metals and semiconductors can facilitate access to unexplored
phenomena and applications. Here we combine electrostatic self-assembly
and Cd<sup>2+</sup>/Cu<sup>+</sup> cation exchange to obtain an anisotropic
coreāshell nanoparticle cluster (NPC) whose optical properties
stem from two dissimilar plasmonic materials: a gold nanorod (AuNR)
core and a copper selenide (Cu<sub>2ā<i>x</i></sub>Se, <i>x</i> ā„ 0) supraparticle shell. The spectral
response of the AuNR@Cu<sub>2</sub>Se NPCs is governed by the transverse
and longitudinal plasmon bands (LPB) of the anisotropic metallic core,
since the Cu<sub>2</sub>Se shell is nonplasmonic. Under aerobic conditions
the shell undergoes vacancy doping (<i>x</i> > 0), leading
to the plasmon-rich NIR spectrum of the AuNR@Cu<sub>2ā<i>x</i></sub>Se NPCs. For low vacancy doping levels the NIR optical
properties of the dually plasmonic NPCs are determined by the LPBs
of the semiconductor shell (along its major longitudinal axis) and
of the metal core. Conversely, for high vacancy doping levels their
NIR optical response is dominated by the two most intense plasmon
modes from the shell: the transverse (along the shortest transversal
axis) and longitudinal (along the major longitudinal axis) modes.
The optical properties of the NPCs can be reversibly switched back
to a purely metallic plasmonic character upon reversible conversion
of AuNR@Cu<sub>2ā<i>x</i></sub>Se into AuNR@Cu<sub>2</sub>Se. Such well-defined nanosized colloidal assemblies feature
the unique ability of holding an all-metallic, a metallic/semiconductor,
or an all-semiconductor plasmonic response in the NIR. Therefore,
they can serve as an ideal platform to evaluate the crosstalk between
plasmonic metals and plasmonic semiconductors at the nanoscale. Furthermore,
their versatility to display plasmon modes in the first, second, or
both NIR windows is particularly advantageous for bioapplications,
especially considering their strong absorbing and near-field enhancing
properties
Quantification of Nanoscale Silver Particles Removal and Release from Municipal Wastewater Treatment Plants in Germany
The majority of pure silver nanoparticles
in consumer products
are likely released into sewer systems and usually end up in wastewater
treatment plants (WWTPs). Research investigating the reduction in
nanoscale silver particles (n-Ag-Ps) has focused on the biological
treatment process, generally in controlled laboratory experiments.
This study, analyzing the field-collected samples from nine municipal
WWTPs in Germany, is the first to evaluate the reduction in n-Ag-Ps
by mechanical and biological treatments in sequence in WWTPs. Additionally,
the concentration of n-Ag-Ps in effluent was determined through two
different methods that are presented here: novel ionic exchange resin
(IER) and cloud point extraction (CPE) methods. The n-Ag-Ps concentrations
in influent were all low (<1.5 Ī¼g/L) and decreased (average
removal efficiency of ā¼35%) significantly after mechanical
treatment, indicating that the mechanical treatment contributes to
the n-Ag-Ps removal. Afterward, more than 72% of the remaining n-Ag-Ps
in the semi-treated wastewater (i.e., wastewater after mechanical
treatment) were reduced by biological treatment. Together, these processes
reduced 95% of the n-Ag-Ps that entered WWTPs, which resulted in low
concentration of n-Ag-Ps in the effluents (<12 ng/L). For a WWTP
with 520000 t/d treatment capacity, we estimated that the daily n-Ag-Ps
load in effluent discharge equated to about 4.4 g/d. Obviously, WWTPs
are not potential point sources for n-Ag-Ps in the aquatic environment
Bulk Synthesis and Structure of a Microcrystalline Allotrope of Germanium (<i>m-allo</i>-Ge)
An easy to reproduce and scale-up method for the preparation of a microcrystalline allotrope of germanium is presented. Based on the report of the oxidation of a single crystal of Li<sub>7</sub>Ge<sub>12</sub> the synthesis and structure determination of a powdered sample of Li<sub>7</sub>Ge<sub>12</sub> is investigated. Besides the known oxidation of Li<sub>7</sub>Ge<sub>12</sub> with benzophenone a variety of protic solvents such as alcohols and water were used as oxidants. Electron energy loss spectroscopy (EELS) proves that the reaction products do not contain Li. The structure determination of the powder samples based on selected area electron diffraction (SAED), powder X-ray diffraction, quantum chemical calculations (DFT-B3LYP level of theory), and simulated powder X-ray diffraction diagrams obtained using the DIFFaX and FAULTS software packages show that the microcrystalline powders do not match any of the existing structures of germanium including the rough model of so-called <i>allo</i>-Ge. It is shown that the structural motif of layered Ge slabs of the precursor Li<sub>7</sub>Ge<sub>12</sub> that contain five-membered rings is retained in <i>m</i>icrocrystalline <i>allo</i>-Ge (<i>m-allo</i>-Ge). The covalent connectivity between the slabs and the statistic of the layer sequence is determined. According to B3LYP-DFT calculations of a periodic approximate model a direct band gap is expected for <i>m-allo-</i>Ge
Fast Characterization of Polyplexes by Taylor Dispersion Analysis
In a single procedure, Taylor dispersion
analysis (TDA) was used
for the size characterization of polyplexes and the quantification
of free polycation contained in excess within the polyplex sample.
TDA analysis was carried out in frontal mode for a better sensitivity
of detection. The proof of concept was established using a model polyplex
generated from the mixture of linear polylysine (DP 20) and DNA from
salmon testes at nitrogen to phosphate (N/P) ratio of 12. Polyplex
hydrodynamic radius was compared to the values obtained by dynamic
light scattering measurements. TDA was found to give access to the
weight-average hydrodynamic radius, while DLS basically gives an intensity-average
(harmonic <i>z</i>-average) value. The method was next applied
to the study of various polyplexes issued from polylysines of various
DP (50, 100) and different topologies (dendrigraft polylysines of
generation 2 and 3). This new methodology should greatly contribute
to the physicochemical characterization of polyplexes used for gene
transfection
Puzzling Intergrowth in Cerium Nitridophosphate Unraveled by Joint Venture of Aberration-Corrected Scanning Transmission Electron Microscopy and Synchrotron Diffraction
Thorough
investigation of nitridophosphates has rapidly accelerated
through development of new synthesis strategies. Here we used the
recently developed high-pressure metathesis to prepare the first rare-earth
metal nitridophosphate, Ce<sub>4</sub>Li<sub>3</sub>P<sub>18</sub>N<sub>35</sub>, with a high degree of condensation >1/2. Ce<sub>4</sub>Li<sub>3</sub>P<sub>18</sub>N<sub>35</sub> consists of an
unprecedented
hexagonal framework of PN<sub>4</sub> tetrahedra and exhibits blue
luminescence peaking at 455 nm. Transmission electron microscopy (TEM)
revealed two intergrown domains with slight structural and compositional
variations. One domain type shows extremely weak superstructure phenomena
revealed by atomic-resolution scanning TEM (STEM) and single-crystal
diffraction using synchrotron radiation. The corresponding superstructure
involves a modulated displacement of Ce atoms in channels of tetrahedra
6-rings. The displacement model was refined in a supercell as well
as in an equivalent commensurate (3 + 2)-dimensional description in
superspace group <i>P</i>6<sub>3</sub>(Ī±, Ī²,
0)Ā0Ā(āĪ± ā Ī², Ī±, 0)Ā0. In the second
domain type, STEM revealed disordered vacancies of the same Ce atoms
that were modulated in the first domain type, leading to sum formula
Ce<sub>4ā0.5<i>x</i></sub>Li<sub>3</sub>P<sub>18</sub>N<sub>35ā1.5<i>x</i></sub>O<sub>1.5<i>x</i></sub> (<i>x</i> ā 0.72) of the average structure.
The examination of these structural intricacies may indicate the detection
limit of synchrotron diffraction and TEM. We discuss the occurrence
of either Ce displacements or Ce vacancies that induce the incorporation
of O as necessary stabilization of the crystal structure
Bending Gold Nanorods with Light
V-shaped
gold nanoantennas are the functional components of plasmonic
metasurfaces, which are capable of manipulating light in unprecedented
ways. Designing a metasurface requires the custom arrangement of individual
antennas with controlled shape and orientation. Here, we show how
highly crystalline gold nanorods in solution can be bent, one-by-one,
into a V-shaped geometry and printed to the surface of a solid support
through a combination of plasmonic heating and optical force. Significantly,
we demonstrate that both the bending angle and the orientation of
each rod-antenna can be adjusted independent from each other by tuning
the laser intensity and polarization. This approach is applicable
for the patterning of V-shaped plasmonic antennas on almost any substrate,
which holds great potential for the fabrication of ultrathin optical
components and devices
<i>In Situ</i> SAXS Study on a New Mechanism for Mesostructure Formation of Ordered Mesoporous Carbons: Thermally Induced Self-Assembly
A new mechanism for mesostructure formation of ordered
mesoporous
carbons (OMCs) was investigated with in situ small-angle X-ray scattering
(SAXS) measurements: thermally induced self-assembly. Unlike the well-established
evaporation-induced self-assembly (EISA), the structure formation
for organicāorganic self-assembly of an oligomeric resol precursor
and the block-copolymer templates Pluronic P123 and F127 does not
occur during evaporation but only by following a thermopolymerization
step at temperatures above 100 Ā°C. The systems investigated here
were cubic (<i>Im</i>3Ģ
<i>m</i>), orthorhombic <i>Fmmm</i>) and 2D-hexagonal (plane group <i>p</i>6<i>mm</i>) mesoporous carbon phases in confined environments, as
thin films and within the pores of anodic alumina membranes (AAMs),
respectively. The thin films were prepared by spin-coating mixtures
of the resol precursor and the surfactants in ethanol followed by
thermopolymerization of the precursor oligomers. The carbon phases
within the pores of AAMs were made by imbibition of the latter solutions
followed by solvent evaporation and thermopolymerization within the
solid template. This thermopolymerization step was investigated in
detail with in situ grazing incidence small-angle X-ray scattering
(GISAXS, for films) and in situ SAXS (for AAMs). It was found that
the structural evolution strongly depends on the chosen temperature,
which controls both the rate of the mesostructure formation and the
spatial dimensions of the resulting mesophase. Therefore the process
of structure formation differs significantly from the known EISA process
and may rather be viewed as thermally induced self-assembly. The complete
process of structure formation, template removal, and shrinkage during
carbonization up to 1100 Ā°C was monitored in this in situ SAXS
study
Nanocellulose-Assisted Formation of Porous Hematite Nanostructures
We report the formation of porous
iron oxide (hematite) nanostructures
via solāgel transformations of molecular precursors in the
confined space of self-organized nanocrystalline cellulose (NCC) used
as a shape-persistent template. The obtained structures are highly
porous Ī±-Fe<sub>2</sub>O<sub>3</sub> (hematite) morphologies
with a well-defined anisotropic porosity. The character of the porous
nanostructure depends on the iron salt used as the precursor and the
heat treatment. Moreover, a postsynthetic hydrothermal treatment of
the NCC/iron salt composites strongly affects the crystal growth as
well as the porous nanomorphology of the obtained hematite scaffolds.
We demonstrate that the hydrothermal treatment alters the crystallization
mechanism of the molecular iron precursors, which proceeds via the
formation of anisotropic iron oxyhydroxide species. The nanocellulose
templating technique established here enables the straightforward
fabrication of a variety of mesoporous crystalline iron oxide scaffolds
with defined porous structure and is particularly attractive for the
processing of porous hematite films on different substrates
Connecting Composition-Driven Faceting with Facet-Driven Composition Modulation in GaAsāAlGaAs CoreāShell Nanowires
Ternary
IIIāV alloys of tunable bandgap are a foundation
for engineering advanced optoelectronic devices based on quantum-confined
structures including quantum wells, nanowires, and dots. In this context,
coreāshell nanowires provide useful geometric degrees of freedom
in heterostructure design, but alloy segregation is frequently observed
in epitaxial shells even in the absence of interface strain. High-resolution
scanning transmission electron microscopy and laser-assisted atom
probe tomography were used to investigate the driving forces of segregation
in nonplanar GaAsāAlGaAs coreāshell nanowires. Growth-temperature-dependent
studies of Al-rich regions growing on radial {112} nanofacets suggest
that facet-dependent bonding preferences drive the enrichment, rather
than kinetically limited diffusion. Observations of the distinct interface
faceting when pure AlAs is grown on GaAs confirm the preferential
bonding of Al on {112} facets over {110} facets, explaining the decomposition
behavior. Furthermore, three-dimensional composition profiles generated
by atom probe tomography reveal the presence of Al-rich nanorings
perpendicular to the growth direction; correlated electron microscopy
shows that short zincblende insertions in a nanowire segment with
predominantly wurtzite structure are enriched in Al, demonstrating
that crystal phase engineering can be used to modulate composition.
The findings suggest strategies to limit alloy decomposition and promote
new geometries of quantum confined structures
A Photoactive Porphyrin-Based Periodic Mesoporous Organosilica Thin Film
A novel
optoelectroactive system based on an oriented periodic mesoporous
organosilica (PMO) film has been developed. A tetra-substituted porphyrin
silsesquioxane was designed as a precursor, and the porphyrin macrocycles
were covalently incorporated into the organosilica framework without
adding additional silica sources, using an evaporation-induced self-assembly
process. The synthesized PMO film has a face-centered orthorhombic
porous structure with a 15 nm pore diameter. This large pore size
enables the inclusion of electron-conducting species such as [6,6]-phenyl
C<sub>61</sub> butyric acid methyl ester in the periodic mesopores.
Optoelectronic measurements on the resulting interpenetrating donorāacceptor
systems demonstrate the light-induced charge generation capability
and hole-conducting property of the novel porphyrin-based PMO film,
indicating the potential of PMO materials as a basis for optoelectroactive
systems